An electric machine such as an electrical motor, power generation system, genset, or the like, is generally used to convert one form of energy into another and may operate in a motoring mode to convert electrical input into rotational or otherwise mechanical output, or operate in a generating mode to convert rotational or otherwise mechanical input into electrical output. Among the various types of machines available for use with an electric drive, switched reluctance (SR) machines have received great interest for being robust and cost-effective. While currently existing systems and methods for controlling such electric machines may provide adequate control, there is still room for improvement.
Among other factors, proper determination of the position and speed of the rotor of the SR machine during relatively low speed operations may have significant impacts on overall performance and efficiency. Some conventional control schemes rely on mechanically aligned speed wheels and sensors to detect and determine the position of the rotor relative to the stator at machine standstill or low speed operations. However, such sensor-based control schemes typically require costly implementations and are susceptible to error. For instance, an error of 2 degrees in the detected mechanical rotor position of an SR machine, caused by a skewed sensor, a mechanical misalignment of the speed wheel, or the like, may correspond to a 0.5% decrease in efficiency of the electric drive assembly at full load.
Although sensorless solutions also exist, conventional sensorless control schemes must implement two or more distinct processes for different ranges of operating speeds or operating modes. For instance, a conventional control scheme for low speed operations, such as that of U.S. Pat. No. 5,525,886 to Lyons, et al., may inject current signals and refer to lookup maps to estimate the rotor position, while a conventional control scheme for high speed operations may apply observers to phase currents to emulate and determine the rotor position. Such a need to simultaneously operate between distinct processes depending on the speed or mode of operation can be inefficient, cumbersome and unnecessarily waste computational resources.
In addition, although the lookup tables or maps used during low speed processes can quickly output the rotor position based on injected current signals, the accuracy of the rotor position at the output is only as good as the quality of the current signal that is read at the input. More specifically, because lookup tables or maps are not capable of sufficiently filtering out noise or distinguishing errors induced by noise from the targeted signal, the rotor position ultimately output can be based on noise-induced errors and thus susceptible to inaccuracies. Furthermore, while conventional systems typically derive rotor speed based on the rotor position, derivations or calculations based on noisy rotor position information can further compound noise-induced errors, output even noisier rotor speed information, and adversely impact the overall performance of the associated SR machine.
Accordingly, there is a need to provide control schemes for controlling SR machines that are not only less costly and easier to implement, but also more efficiently performed without compromising overall reliability. Moreover, there is a need to provide a simplified control system or a single unified control scheme that can operate across wider ranges of operating speeds or operating modes of an SR machine and consume less of the computational resources allocated for use with the SR machine. There is also a need to provide a solution that is more reliable and robust to noise, all without requiring additional computational resources or proximity sensors. The systems and methods disclosed herein are directed at addressing one or more of the aforenoted needs.